Printing systems of a variety of types and kinds are well known and commonly used in the production of print jobs that include numerous marked or printed sheets of media. Often, these marked or printed sheets of media are grouped or otherwise separated into two or more sets that together form a given print job. In some cases, the individual sets of marked sheets of media are simply grouped together and output as a stack of sets, such as by staggering the alignment of adjacent sets, for example. In other cases, however, the print job will include an instruction to perform one or more finishing operations on each individual set. Examples of such finishing operations can include hole punching and stapling or stitching operations.
One result of including such a finishing instruction for one or more of the sets of a print job is that each set that is to undergo a finishing operation will take some additional amount of processing time for the finishing operation to be completed. In some cases, this additional amount of processing time may result in only a relatively small or otherwise minor increase in the overall production time of the print job. This can be particularly true in cases in which the sets of the print job include a significant number of printed sheets (e.g., twenty or more marked sheets of media). As an example, a set that includes fifty marked sheets of media can be generated on a printing system that operates at an imaging rate of fifty pages per minute in a time period of about sixty seconds. The performance of a finishing operation (e.g., a stapling or stitching operation) may add only two or three seconds to the overall production time, which represents an increase of about 3-5 percent over the sheet production time. In many cases, this additional amount of time may be deemed to be a relatively modest and, thus, acceptable increase in the overall production time for the convenience of producing a set of marked sheets of media that is in a finished condition.
In other situations, however, a print job may be made up of two or more sets that include a relatively small number of marked sheets of media (e.g., two to ten marked sheets of media). In these cases, the seemingly modest increase in time contributed by a finishing operation can result in a substantial increase in the overall production time of a set. As an example, the printing of a set of five marked sheets could be generated on a printing system having an imaging rate of fifty pages per minute in a time period of about six seconds. The performance of a finishing operation on such a set of marked sheets of media could add a further two to three seconds to the overall production time. This additional finishing time can represent an increase of between 30 and 50 percent of the sheet production time. In many cases, this increase may be deemed a substantial and undesirable increase in the overall production time.
Additionally, it is common for the finishing unit of known printing systems to include a compiling device that is incapable of receiving individual sheets of media while a finishing operation is being performed thereby. That is, routing additional sheets of media to a compiling device of known finishing units while a finishing operation is being performed thereby is generally avoided as such an action would undesirably affect or otherwise interfere with a stapling, stitching or other operation that is being performed by the compiling device. As such, known finishing units do not generally receive marked sheets of media for compiling during the period (e.g., two to three seconds) that the finishing operation is being performed.
In some cases, a printing system may include a sheet buffering unit or other such device and marked sheets of media can be advanced into such a unit or device during the period that the finishing operation is being performed. In many other cases, however, such a sheet buffering unit or other device will not be included as part of the printing system. So, the media transport pathway of the printing system may not be able to advance marked sheets of media under such circumstances. One possible option under such operating conditions is to simply pause or otherwise discontinue operation of the other portions of the printing system while the finishing operation is performed. There are, however, numerous disadvantages to operating a printing system in such a manner. Such as, for example, the result that the printing system would be inoperative for a substantial period of time, particularly, during production of sets having a relatively small number of marked sheets of media, as discussed above.
Another characteristic that is common to many known printing systems is that the operation of the media transport pathway extending through the printing system is synchronized with the operation of the one or more marking units thereof. Thus, another option for operating under the above-described conditions is to permit the media transport pathway and marking engine to continue to operate in a substantially continuous manner. However, rather than feeding a continuous stream of individual sheets of media to the one or more marking engines, one or more sheet-sized spaces are selectively provided within in the stream of individual sheets traveling along the media transport pathway. Such spaces are often referred to in the art as “skipped pitches.” As a series of one or more skipped pitch approaches an associated marking unit, a corresponding number of one or more imaging cycles is skipped by the marking unit. The printing system typically coordinates the provision of these skipped pitches such that the same reach the finishing unit at approximately the same time that a finishing operation is to be performed. In this manner, the printing system can continue to operation during the period that the finishing operation is being performed.
While the foregoing and other methods of operation may have advantages over other options for operating a printing system, the one or more marking units are, nonetheless, operating at a decreased imaging capacity. And, as discussed above, productivity and output can be particularly decreased for print jobs in which numerous sets to be produced that include only a small number of individual sheets of media.
Accordingly, it is believed desirable to develop a finishing unit, printing system and method of performing a print job that overcome the foregoing and other issues.